Airplane Rounded Body
First of all, model the differences in the x dimension; the tail is never as thick as the fuselage. go into edit-mode and scale the faces of the tail on the x axis. (S+X) you may need to hit O to maintain a good profile while scaling. 

Next go in and select the top and bottom side edges of the tail and in the options on the right (N) turn up the Mean Crease to 1.00. This will make sure that as the side is smoothed, the profile is not lost.

Based on your second screen shot, I would say that you have included the entire side of the fuselage as one N-Gon: you need quads for sub-surf to work efficiently. You can go in and break the large n-gon up by selecting opposing vertices and hitting J. Now you can successfully add a subdivision surface modifier without getting unexpected results.

I will add screen shot when i get home :) hold on; they're coming.